696 research outputs found
Weekly reports for R.V. Polarstern expedition ANT-XXIX/7 (2013-08-14 - 2013-10-16, Punta Arenas - Cape Town), German and English version
Weekly reports for R.V. Polarstern expedition PS112 (2018-03-18 - 2018-05-06, Punta Arenas - Punta Arenas), English version
Cumulant expansions for atmospheric flows
The equations governing atmospheric flows are nonlinear. Consequently, the
hierarchy of cumulant equations is not closed. But because atmospheric flows
are inhomogeneous and anisotropic, the nonlinearity may manifest itself only
weakly through interactions of mean fields with disturbances such as thermals
or eddies. In such situations, truncations of the hierarchy of cumulant
equations hold promise as a closure strategy.
We review how truncations at second order can be used to model and elucidate
the dynamics of atmospheric flows. Two examples are considered. First, we study
the growth of a dry convective boundary layer, which is heated from below,
leading to turbulent upward energy transport and growth of the boundary layer.
We demonstrate that a quasilinear truncation of the equations of motion, in
which interactions of disturbances among each other are neglected but
interactions with mean fields are taken into account, can capture the growth of
the convective boundary layer even if it does not capture important turbulent
transport terms. Second, we study the evolution of two-dimensional large-scale
waves representing waves in Earth's upper atmosphere. We demonstrate that a
cumulant expansion truncated at second order (CE2) can capture the evolution of
such waves and their nonlinear interaction with the mean flow in some
circumstances, for example, when the wave amplitude is small enough or the
planetary rotation rate is large enough. However, CE2 fails to capture the flow
evolution when nonlinear eddy--eddy interactions in surf zones become
important. Higher-order closures can capture these missing interactions.
The results point to new ways in which the dynamics of turbulent boundary
layers may be represented in climate models, and they illustrate different
classes of nonlinear processes that can control wave dissipation and momentum
fluxes in the troposphere.Comment: 43 pages, 10 figures, accepted for publication in the New Journal of
Physic
Antarctic marine life under pressure
Next week, the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) convenes in Hobart, Tasmania, to examine the state of marine life in the Southern Ocean. As part of the Antarctic Treaty System, this convention entered into force in 1982, and its focus on the region’s environmental integrity has never been more important, given the increasing effects of climate change and commercial fishing. An important focus over the past 40 years has been Antarctic krill,
Euphausia superba
(hereafter krill), a keystone species that helps to hold this marine ecosystem together. Climate and fishing stresses should prompt the CCAMLR to address whether management of krill fishing is at a level that protects the Southern Ocean from losing its overall balance of marine life and the oceanic processes that regulate global climate.
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Timing requires the right amount and type of light
The quantity of UVA/deep violet light varies seasonally and affects locomotor activity in a marine annelid, providing cues for phenology in addition to those provided by change in photoperiod
Weiterentwicklung zwingend
Sonderregelungen sind bei einer ökologischen Steuerreform im nationalen Vorausgang notwendig und sinnvoll. Allerdings weisen die in Deutschland realisierten Sonderregelungen gravierende und im Zeitverlauf zunehmende Nachteile auf. Eine Reform tut Not und ist im Rahmen der Weiterentwicklung der Ökosteuer eigentlich auch noch für diesen Sommer vorgesehen. Allerdings gibt es auch bei den möglichen Alternativen keinen Königsweg
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